Solid propellant charges for rocket motors are typically cast to provide a tubular shape that includes a centerport. A centerport is a hollow channel positioned in the approximate center of propellant charge that extends axially throughout the length of the tubular shaped propellant. Generally, a centerport is included to provide stress relief to the cured propellant. A completely solid propellant with no centerport has a strong tendency to form cracks when subjected to changes in temperature. Cracks in the propellant charge are undesirable because cracks will typically cause an uneven burn at the ground base. To avoid the formation of these uncontrolled cracks, a centerport is included. For reasons well known in the art, it is important to protect the centerport from burning during the firing of the propellant. A centerport inhibitor protects the propellant at the inside surface of the centerport from exposure to the flames and/or heat from the burn that is occurring at the ground base of the propellant. This is typically accomplished by utilizing an inhibiting medium, sometimes referred to as a centerport inhibitor.
Traditional centerport inhibitors involve the installation and bonding of an inert material to the centerport, sometimes referred to as a rubber boot. Traditional rubber boots are basically pre-formed, cured rubber sleeves. Both the use and installation of a rubber boot to the centerport has many drawbacks. First, because they are pre-cured, installation of a traditional rubber boot into a centerport is difficult and labor intensive. The installation of a rubber boot is accomplished by one of two ways: either the rubber boot is placed into the centerport of a cured solid propellant and glued into place using an adhesive. Alternatively, the rubber boot can be placed around the tooling of a propellant mold prior to casting the liquid pre-cured propellant and, thereafter, curing the propellant with the rubber boot already in position. In many instances, a third material must be included as part of the installation of the rubber boot, e.g., an additional barrier coat is applied between the glue or adhesive and the propellant in order to prevent the glue or adhesive from leaching into the propellant at the inside surface of the centerport.
Another drawback to the pre-cured rubber boot centerport inhibitor is its tendency to de-bond from the propellant to which it is glued or adhered. When a de-bond of the rubber boot occurs, flames and/or heat may reach the area of the propellant that the inhibitor is designed to protect, specifically the inner surface of the centerport. If the walls of the centerport ignite, the rocket is negatively impacted. At a minimum, this negatively impacts the operation of the rocket motor. However, there is a possibility that such an occurrence may cause the motor to explode.
Therefore, there is a need for a centerport inhibitor that overcomes the disadvantages of prior centerport inhibitors. There is a need for a centerport inhibitor that is easily applied to a cured propellant charge that bonds chemically to the surface of the centerport.